Add missing next() call in Mongoose pre-save middleware hook (Issue #699)

Ensure proper middleware chain execution by calling next() in the pre-save hook. This prevents middleware chain interruption and ensures subsequent hooks are invoked correctly.

Changes:
- Added next parameter to pre-save hook
- Call next() when password modification check returns early
- Call next() at end of middleware to allow next hook execution
- Maintains compatibility with Mongoose middleware chain

Fixes #699

Author: anshul23102

backend/models/User.js

@@ -18,12 +18,12 @@ const UserSchema = new mongoose.Schema({
   },
 });
 
-// ✅ FIXED: no next()
-UserSchema.pre('save', async function () {
-  if (!this.isModified('password')) return;
+UserSchema.pre('save', async function (next) {
+  if (!this.isModified('password')) return next();
 
   const salt = await bcrypt.genSalt(10);
   this.password = await bcrypt.hash(this.password, salt);
+  next();
 });
 
 // ✅ password comparison